1. Field of the Invention
This invention relates to magnetic recording mediums such as magnetic audio or video tapes, and magnetic disks such as floppy disks and hard disks. More particularly, the invention relates to an improvement in such mediums in which a specific type of modified vinyl chloride resin is used as a binder for the magnetic recording layer. The modified vinyl chloride resin may also be used as a binder for the back coat layer of such mediums.
2. Description of the Prior Art
A diversity of magnetic recording mediums, such as magnetic tapes and magnetic disks, have been proposed and are, in fact, in use. These magnetic recording mediums are, in most cases, fabricated by applying a magnetic paint containing magnetic powder, a binder resin and other additives onto a non-magnetic support and drying the applied paint to form a magnetic layer on the support. In these magnetic recording mediums, the binder resin greatly influences magnetic characteristics of the medium, the durability of the magnetic layer, and the electromagnetic conversion characteristics. Accordingly, studies have been extensively made on the binder resin by modification of existing resins.
For instance, Japanese Laid-open Patent Application No. 60-238309 describes a modified vinyl chloride resin for use as a binder for magnetic recording mediums. This vinyl chloride resin is obtained by copolymerizing a vinyl chloride monomer, a monomer having an alkali metal or ammonium salt of a strong acid containing sulfur or phosphorus, and a monomer having an epoxy group with or without other monomers copolymerizable with these monomers. The magnetic recording medium using this specific type of vinyl chloride resin as a binder of the magnetic layer shows some effects of improving characteristic properties but has not been found to be satisfactory.